Technological Field
The present invention relates to an image forming apparatus.
Description of Related Art
In general, an image forming apparatus (such as a printer, a copier, and a facsimile machine) using an electrophotographic processing technique applies (exposes) laser light on the basis of image data to a charged photoconductor drum (image bearing member) to form an electrostatic latent image. In the image forming apparatus, a developing unit supplies toner to the photoconductor drum provided with the electrostatic latent image to visualize the electrostatic latent image to form a toner image. The image forming apparatus further primarily or secondarily transfers the toner image to a sheet and heats and pressurizes the sheet by a fixing nip of a fixing unit to fix the toner image on the sheet. Some image forming apparatus include registration rollers that are disposed upstream of a transfer section, which transfers an image onto a sheet, and correct a positional deviation of the sheet in the width direction thereof, as described, for example, in Japanese Patent Application Laid-Open No. 2014-133634 (hereinafter referred to as PTL 1) and Japanese Patent Application Laid-Open No. 2013-91563 (hereinafter referred to as PTL 2).
By the way, the image forming apparatus has a problem of occurrence of a phenomenon (sub scanning obliqueness) in that a conveyance direction of the sheet is passed obliquely in a sub scanning direction due to misalignment from the registration rollers to the fixing nip through the secondary transfer nip. In addition to the case of the misalignment, the sub scanning obliqueness is likely to occur when there is a difference between the diameters at opposite ends of the rollers in the sheet width direction (sub scanning direction) due to a durability issue or the like. A long sheet with a long size in the conveyance direction is easily affected, and the sub scanning obliqueness often occurs. The sub scanning obliqueness leads to a poor image due to deviation, distortion, or the like of the image transferred at the transfer section, and a technique for reducing the sub scanning obliqueness is demanded.
In contrast, PTL 1 and other references each describe a technology for registration displacement control in which a line sensor is disposed between the registration rollers and the transfer rollers, the line sensor senses the position of the width-direction end (side end) of a sheet while the transfer rollers convey the sheet, and the registration rollers are moved based on the result of the sensing.
In the technology described in PTL 1 and other references, however, the line sensor senses deviation of the side end of a sheet from the reference position, the amount of displacement of the registration rollers is determined from the result of the sensing, and the registration rollers are displaced based on the determined value. The side end of the sheet therefore deviates from the reference position in some cases when the displacement is stopped.